Tube coating apparatus

ABSTRACT

TUBE FORMING APPARATUS COMPRISING A STATIONARY CANTILEVER ARBOR HAVING A FREE END AND MEANS FOR CONTINUOUSLY WRAPPING STRIP-SHEET MATERIAL ABOUT THE ARBOR CONTINUOUSLY TO FORM A TUBE AND ADVANCE THE TUBE BEYOND THE FREE END, A TUBE COATING UNIT MOUNTED ON THE FREE END OF THE ARBOR FOR COATING THE INTERIOR SURFACE OF THE FORMED TUBE AS IT CONTINUOUSLY ADVANCES BEYOND SAID FREE END, AND COATING DRYING APPARATUS INCLUDING A DRYING HEAD   DEFINING A PLURALITY OF AXIALLY AND RADIALLY-SPACED, RADIALLY-FACING DRYING APERTURES AND MEANS FOR SUPPLYING DRYING AIR TO SAID DRYING HEAD.

'1971 H. c. ALLEN ETAL TUBE COATING APPARATUS 2 Sheets-Sheet l Filed April 18. 1968 H. c. ALLEN ETAL TUBE COATING APPARATUS Jan. 26; v197-1 2 Sheets-Sheet 2 Filed April 18. 1968 1"? WT I '1 'I I l ll IMQ mm a Q M 3+ United States Patent 3,558,402 TUBE COATING APPARATUS Herman Curtis Allen, Medford, and Charles Arthur De Virgilio, Roslindale, Mass., assignors to Bird &

Son, Inc., East Walpole, Mass., a corporation of Massachusetts Filed Apr. 18, 1968, Ser. No. 722,303 Int. Cl. B31c 3/00, 11/04 US. Cl. 156425 20 Claims ABSTRACT OF THE DISCLOSURE This invention relates to coating apparatus and more particularly, to apparatus for coating the inside of wrapped paper tubes or other tubing with a coating material.

The interior cylindrical surfaces of wrapped paper tubes are not completely uniform. The seam structure and finish of the paper forming the tube vary, the cut edges of the paper stripping is uncalendered, and small surface fibers may be raised as a result of dragging the stripping over the wrapping mandrel. These variations and non-uniformities are of little consequence until one tries to apply a uniform coating to the interior of the wrapped tube. Then, although it is relatively easy to coat the smooth sides of the paper stripping uniformly, the absorption of the cut edge of the stripping, seepage between lapped plies of stripping and the inherent nonuniformity of the seams between adjacent turns of stripping make it extremely dilficult to apply, dry cure/ and fuse a uniform coating over the entire interior surface of the tube. This problem is especially acute when the coating is applied as part of a continuous operation in which the tube is first wrapped at relatively high line speeds.

Accordingly, it is a primary object of the present invention to provide for apparatus for coating the inside of a wrapped paper tube with a layer of a preselected material, a means and method for drying and curing the layer in a controlled manner immediately after it is applied. Other objects include providing means for use in combination with apparatus for forming paper tubing by continuously wrapping paper stripping about a stationary arbor for coating the inside of a paper tube with any desired thickness of a coating material and providing apparatus of the type mentioned which includes means for controlling the thickness of the coating by varying the diameter of the wiper or doctor element and means for closely controlling the temperature of the coating material and for eliminating bubbles or impurities in the coating material.

Generally speaking, the invention utilizes at least one coating and drying unit mounted coaxially with and beyond the free end of the arbor. The unit includes an applicator mounted between a doctor and the free end of the stationary arbor and tube drying apparatus on the side of the doctor opposite the arbor. The drying apparatus includes a drying head defining a plurality of 3,558,402 Patented Jan. 26, 1971 axially and radially-spaced apertures for directing streams of drying air in directions generally normal to the tube. In preferred embodiments, in which a number of coating and drying units may be mounted in coaxial succession, the apertures are regularly spaced and discharge air into substantially closed drying chambers, and the apparatus includes means for carefully controlling the temperature of the coating material.

Other objects, advantages and features will appear from the following description of a preferred embodiment of the invention, taken together with the accompanying drawings, in which:

FIG. 1 is an oblique foreshortened view of tube forming apparatus which includes tube coating means embodying a preferred form of the present invention;

FIG. 2 is a plan view of conventional tube wrapping apparatus;

FIG. 3 is a sectional view taken at 3-4 of FIG. 1;

FIG. 4 is a plan view, partially in section, of the apparatus of FIG. 1;

FIG. 5 is a diagramatic view of portions of the apparatus of FIG. 1;

FIG. 6 is a sectional view taken at 66 of FIG. 3; and

FIG. 7 is a sectional view of tubing coated using the apparatus of FIG. 1.

Referring now to the drawings, there is illustrated means for coating the interior peripheral surface of a paper tube 12 with a coating material, such as an organic plastic, immediately after the tube is formed by wrapping paper stripping 14 in a helical configuration about a stationary tube-forming arbor 16. The coating means comprises two coating and drying units 10, 11 mounted coaxially on the free end of arbor 16 forming, in effect, an extension of the arbor.

The conventional means for wrapping the paper stripping 14 into a tube 12 (see FIG. 2) comprises in addition to the smooth, tube forming arbor 16, a pair of spindles 18 spaced on opposite sides of arbor 16 with their axis perpendicular to the axis of arbor 16, a continuous belt 20 entrained about the arbor and spindles, and means (not shown) for driving at least one of the spindles in rotation. The belt is wrapped about the arbor at an angle (to the axis of the rabor) equal to the angle at which the tube is to be helically wrapped. The paper stripping 14 is fed between belt 20 and arbor 16 at this same angle and is spirally wrapped about the arbor in spaced, abutting or overlapping helical convolutions or configuration by the moving belt. One or several overlying layers of paper may be similarly applied to provide a multi-layer tube.

As the tube 12 is formed from stripping 14, it rotates and moves axially along the arbor, away from the belt and spindles and over coating units 10, 11. Typically, the tube is advanced axially at speeds up to feet per minute.

As illustrated most clearly in FIGS. 4-6, each coating unit 10, 11 comprises a circumferentially grooved applicator ring 26, an inflatable cylindrical wiper or doctor element 28 slightly spaced from said ring on the side thereof most distant from arbor 16 to form an overflow reservoir 30 intermediate ring 26 and doctor 28, means for supplying and recirculating the coating material, and a plurality of radially-extending drying jets -32 on the side of the doctor 28 most distant from arbor :16. Each of units 10, 11 applies a layer of coating material of predetermined thickness to the inside of tube 12; unit 11 applying its layer on top of the layer previously applied by unit 10. In each unit, the liquid coating material is initially applied in liquid form by ring 3 26, smoothed by doctor 28, and the layer dried and cured by air from jets 32.

The applicator ring 26 of each unit includes a circumferential groove 34, providing a principal coating reservoir, defined by a pair of axially spaced, radially-extending, circumferential flanges 36 and 38. The flange 36 closest the free end of arbor 16, has a diameter substantially equal to the inside diameter of tube 12. Flange 38 on the other side of groove 34, has a slightly smaller diameter to provide a clearance between the flange and the inside of the tube. The amount of clearance, which should be slightly more than the desired final thickness of the coating, depends primarily on the viscosity of the particular material used in the coating process. Typically, the clearance will be approximately 0.005 in.

The toroidal doctor element 28 of each unit is mounted on a hub 40. The opposite axial ends of the doctor are pressed tightly against the adjacent ends of the hub by a circular plate 44 on the side of hub farthest from arbor 16 and a cylindrical spacer 46 between ring 26 and hub 40 thereby providing the required substantially air-tight seal. As more clearly shown in FIG. 6, the circumferential surface of spacer 46 forms the base of reservoir 30, the sides of which are formed by the adjacent surfaces of doctor 28 and flange 38 of ring 26.

The coating unit 11 farthest from arbor 16 also includes a flexible rubber gland 33 mounted coaxially with ring 26 on the side thereof nearest arbor 16 to prevent liquid coating in unit 11 from flowing into the drying and curing area of unit 10. As illustrated, gland 33 comprises a cylindrical disc having an outside diameter slightly greater than the inside diameter of tube 14 and is secured in position by the adjacent axially-facing surface of ring 26 and circular gland mounting plate 122.

As shown in FIG. 5, circumferential groove 34 and overflow reservoir include coating material inlet and return flow ports to insure proper circulation of the coating material. In the illustrated embodiment, an inlet port 48 and a return port 50 spaced 180 opposite inlet port 48 are provided in each groove 34; a second return 52 is provided in each overflow reservoir 30 spaced 90 from inlet port 48 and return port 50. An inlet 42 for providing air under pressure to inflate doctor 28 to the desired size and pressure is provided in each hub at a point circumferentially spaced 180 from return port 52.

As illustrated in FIG. 5, the coating material is initially provided in a supply tank (not shown); and is forced under pressure from the tank, through a coating material supply conduit 56 extending through arbor 16, and

into circumferential grooves 34 in rings 26 through the inlet ports 48 therein. A pump 58 provides the pressure, typically zero to twenty p.s.i., required to fill groove 34 and maintain a supply of coating material in contact with the inside wall of tube 12, also includes filtration means for removing impurities from the coating material. The pressure, in conjunction with the movement of the formed tube 12 as it moves axially away from forming arbor 16, causes some coating material to flow into and at least partially fill overflow reservoirs 30, along with the coating material doctored ofl by the inflatable doctor. This coating material flows back to the supply tank through coating material return conduits 60 and 62 extending from return ports and 52, respectively, and providing for the desired continuous recirculation of the coating material.

The various components of the coating apparatus may become quite warm when in use. In previous coating apparatus, this heat has been extremely troublesome, causing some of the coating material to break down or in the case of an organic material to partially polymerize, thereby forming undesirable lumps, fibers, or other impurities. To maintain the temperature of the coating material in the desired range, i.e., warm enough to flow smoothly and cool enough to avoid breakdown or polymerization, irrespective of variat o s in the temperature of the wrapping, coating and drying apparatus, water jackets are provided surrounding coating material supply conduit 56 and return conduits 60, 62. As shown in FIGS. 4 and 6, a supply conduit water jacket 57 and return conduit supply jackets 61, 63 extend from within arbor 16 to a cylindrical water manifold or header 70 mounted coaxially with units 10, 11 on the side of unit 11 farthest from arbor 16. Header 70, which is hollow, has a diameter approximately inch less than that of arbor 16 thereby providing approximately inch clearance between the header and the wrapped tube. Openings communicating with the cavity within header 70 are provided in the side walls of water jackets 57, 61, 63. An inlet pipe 73 extends from a temperature-controlled water source (not shown) to the end of supply conduit water jacket 57 adjacent arbor 16. A by-pass line 74 including a by-pass valve 76 extends from inlet pipe 72 to coating supply conduit 56 for directing water into the coating conduits to flush the system. A common outflow fitting 78 connects the ends of return conduit water jackets 61, 63 to an outflow pipe 80. In practice, water at a predetermined temperature is forced at a controlled rate into water jacket 59, flows the length of jacket 59 into header 70, from header 70 into water jackets 61, 63 and thence from the other ends of jackets 61, 63 into outflow pipe 80.

As shown in FIG. 5, a second water cooling system is provided to cool the wrapping mandrel of arbor 16. Wrapping and drawing paper stripping therearound imports a considerable amount of heat to the mandrel and, if the mandrel were not cooled, the heat would draw glue inwardly through the inner stripping ply and reduce the impregnation of coating material into the ply. The mandrel coating system includes a water chamber 82 within and communicating with the cylindrical wall of arbor 16 and the water inlet 84 and outlet 86 for providing continuous water flow within chamber 82.

For controlling the internal pressure of doctors 28, an air line 64 is provided leading from a supply source (not shown) to the inlets 42 in hubs 40, a regulator 66 for controlling the air flow from the source, and a bleeder system 68 for hydrostatically maintaining exactly the desired pressure are also provided in line 64. Typically, the internal pressure of doctors 28 will be maintained at a predetermined level between zero and twenty p.s.i.

The apparatus for drying the coating on the inside of tube 12 after it is applied by the grooved applicator ring 38 and smoothed by the doctor element 28 of each of units 10, 11 is best illustrated in FIGS. 1, 3 and 4. As shown, a pair of coaxial tubes, air return tube 92 and air supply tube mounted within tube 92, extend from 'water header 70 to air make-up apparatus 94 mounted adjacent the far end of arbor 16. Air make-up apparatus 94 comprises a supply fan 96, an air heater 98, a supply air damper connected to supply tube 90 by supply duct 102, and an exhaust fan 104 connected to return tube 92 through return duct 106.

In conjunction with the surrounding portions of tube 16, each of units 10, 11 provides a substantially closed tube drying chamber, generally designated 108, 109, respectively. The peripheral walls of chambers 108, 109 are formed by the portions of tube 12 surrounding units 10, 11. The end walls of chamber 108 are formed by doctor 28 of unit 10 and gland 33 of unit 11; those of chamber 108 by the doctor 28 of unit 10 and water header 70. A plurality of uniformly spaced drying air jets 32 are provided in each of chambers 108, 109. Each jet communicates at its inner ends with supply tube and extends radially outwardly therefrom through openings 110 in the circumferential wall of return tube 90 to a point spaced inwardly, typically about three sixteenths of an inch from the inside wall of tube 16. Each opening 110 in return tube 90 is correspondingly larger in area than is the air jet 32 passing therethrough to provide a return opening through which moisture-laden air may be drawn away from the tube interior. -In operation, exhaust fan 104 draws the moistureladen air from drying chambers 108, 109 at such a rate as to maintain a slight negative pressure in the drying chambers. This negative pressure, in turn, draws fresh drying air into the chambers through air jets 32.

Each unit 10, 11 includes approximately fifteen axially spaced banks 111, 112, respectively, of drying jets. As shown, the four jets 32 of each of banks 111, 112 are circumferentially spaced at 90 intervals and the banks 110, 111 themselves are axially spaced at regular intervals. Typically, spacing between banks is /3 or /2 the distance between adjacent seams of tube 16.

The four air jets 32 in each particular bank are of the same size; the different banks of jets have varying diameters. The diameter of the jets of each bank depends on and varies inversely according to the distance of the particular bank from the doctor element of that unit. For example, in unit 10, the jets of banks 111 nearest doctor 28 are larger than those farther from the doctor. The exact diameter of the jets of each bank is predetermined to insure that all jets in each unit'discharge air perpendicularly to the adjacent surface of tube 14 at substantially the same velocity. The jets 32 in banks 112 of unit 11 are also sized so that the jets of all banks 112 discharge drying air at substantially the same velocity. Depending upon the exact coating material and thickness of the coating applied by unit 11, this velocity may be less, equal to, or greater than the velocity of the drying air emitted by the jets of unit 10.

As previously indicated, one of the major problems in applying uniform coating to the interior surface of wrapped paper tubes is that because of the seam construction, the interior surface of the wrapped tube is not absolutely smooth but, on the contrary, is consistently irregular. When the tube is coated, therefore, the smooth interior surface of the stripping is covered with a layer of one uniform thickness, and the seams are covered with layers of a different, often varying, thickness. This variation, in a butt seam tube, is illustrated in FIG. 7. Moreover, the coating in the area of a butt seam (in which there is a slight spiral space between adjacent turns) has a different configuration than does the coating in the area of a lapped seam. For these reasons diiferent drying and curing rates are required for the smooth interior surface of the. wrapped stripping and the area of the seams. By axially adjusting the point at which paper stripping is introduced into the tube wrapping structure, the operator can vary the amount by which the uniformly spaced drying jets lead or lag the spiral seam and thereby control the rate at which the coating material in each tube area is dryed and cured. This flexibility makes it possible to eliminate the formerly serious problem of dendritic growth in the seam area.

Other embodiments within the scope of the following claims will occur to those skilled in the art.

What is claimed is:

1. For tube forming apparatus comprising:

a stationary cantilever arbor having a free end and means for continuously wrapping strip-sheet material about said arbor continuously to form a tube of said material and advance said formed tube beyond said free end, and,

a tube coating unit mounted on the free end of said arbor for coating the interior surface of said formed tube as it continuously advances beyond said free end, said tube coating unit including doctor means spaced beyond said free end and a reservoir between said free end and said doctor means for maintaining a supply of coating material in contact with the interior surface of the formed tube surrounding said reservoir; that improvement which consists of:

coating drying apparatus including:

a drying head adapted for mounting on the side of said doctor means most distant from said arbor and defining a plurality of axially and radiially-spaced, radially-facing drying apertures; an means for supplying drying air to said drying head. 2. The apparatus of claim 1 wherein said apertures are arranged in banks, said banks being axially spaced at substantially regular intervals.

3. The apparatus of claim 2 wherein the ratio of the distance between successive seams of said tube to the distance between successive banks is xzl and x is substantially equal to a whole number.

. 4. The apparatus of claim 2 wherein each of said banks includes a plurality of aperatures circumferentially spaced at substantially regular intervals.

5. The apparatus of claim 4 wherein all apertures in a given one of said banks are of substantially the same cross-sectional area and the apertures in different ones of said banks are of different cross-sectional areas, said areas being predeterminedly related so that drying air is discharged from all of said apertures at substantially the same velocity. 6. The apparatus of claim 1 wherein said coating drymg apparatus includes an air supply tube extending through said arbor and said unit to a point beyond said doctor means and said apertures are defined by a plurality of air jet tubes extending radially outwardly from said air supply tube and defining said apertures.

7. The apparatus of claim 6 including an air return tube surrounding said air supply tube and extending coaxially therewith, said air return tube including a plurality of openings in the wall thereof, one of said air jet tubes extending radially through each of said openings in said air return tube, and the cross-sectional area of said each opening being greater than that of the air jet tube passing therethrough.

8. The apparatus of claim 7 wherein said air jet tubes are arranged in axially-spaced banks, said banks being spaced at substantially regular intervals.

9. The apparatus of claim 8 wherein each of said banks contains a plurality of air jet tubes circumferentially spaced at substantially equal intervals.

10. The apparatus of claim 9 wherein each of said banks includes four jet tubes.

11. The apparatus of claim 1 wherein said apparatus in conjunction with the portion of said tube therearound defines an axially-extending annular, substantially-closed drying chamber surrounding said drying head.

12. The apparatus of claim 11 wherein said drying head ncludes air return openings and said drying apparatus including air return means communicating with said air return openings for drawing air from said drying chamber.

13. The apparatus of claim 12 wherein said drying apparatus includes an air supply tube extending through said arbor to beyond said doctor means, an air return tube surrounding and extending coaxiall with said air supply tube, and a plurality of air jets tubes extending radially outwardly from said supply tube through openings in the peripheral wall of said air return tube.

14. In tube forming apparatus comprising:

a stationary cantilever arbor having a free end and means for continuously wrapping strip-sheet material about said arbor continuously to form a tube of said material and advance said formed tube beyond said free end;

that improvement which consists of:

a plurality of tube coating units mounted in coaxially succession on the free end of said arbor for coating the interior surface of said formed tube as it continuously advances beyond said free end, each of said tube coating units including:

doctor means;

a principal coating reservoir between said free end and said doctor means for maintaining a supply of coating material in contact with the interior surface of the formed tube surrounding said coating reservoir; and coating drying apparatus including a drying head beyond said doctor means defining a plurality of radially-facing, axially and radially-spaced apertures for directing drying air towards the interior of said tube in directions substantially normal thereto. 15. The apparatus of claim 14 including coating material supply means including a coating supply conduit extending through said arbor to the reservoir of each of said units for maintaining a supply of coating material therein a coating material return conduit extending from the reservoir of each of said units through said arbor, and

coating material temperature control means for transferring heat relative to said conduits to maintain the temperature of the coating material within said conduits within a predetermined range.

16. The apparatus of claim 15 wherein said temperature control means includes tubes mounted coaxialy with and surrounding said conduits and means for circulating fluid at a controlled temperature through said tubes.

17. The apparatus of claim 14 wherein said apertures of each of said units are arranged in axially-spaced banks, the distance between successive banks in each unit being substantially uniform.

18. The apparatus of claim 14 wherein each of said units, in conjunction with the portion of said tube therearound, defines an axially-extending, annular drying chamber surrounding the drying head of the unit.

19. The apparatus of claim 18 wherein each of said drying heads defines air return openings and said drying apparatus includes air return means extending from said air return openings to draw air from said chambers.

20. The apparatus of claim 19 including coaxial air supply and return tubes extending through said arbor to said units, each of said drying heads including air jet tubes extending radially outwardly from said air supply tube through openings in said air return tube.

References Cited UNITED STATES PATENTS BENJAMIN A. BORCHELT, Primary Examiner T. H. WEBB, Assistant Examiner U.S. Cl. X.R. 

